Conventionally, in a vehicle control, when a vehicle operator operates a brake pedal, a target operating amount is set based on an operating characteristic (control map) where a correlation between an operating amount of the brake pedal and a deceleration of the vehicle is defined, and the behavior of the vehicle is controlled based on the target operating amount. Meanwhile, in order to improve an operating feel of the operator, numerous controllers which perform a vehicle control conforming to the operator's sensitivity based on psychophysics are proposed. As expressions of a relationship between the physical quantity and the sensation (perceived intensity) in the form of a function, the Weber-Fechner law and Stevens's power law are known. Fechner's law is a law in which the sensation is proportional to the logarithm of stimulus intensity, and Stevens's law is a law in which the sensation is proportional to a power of the stimulus intensity.
JP2011-143915A does not disclose a braking control device, but does disclose a vehicle control device including an acceleration generator which generates acceleration on a vehicle, and a controller which controls the acceleration generator based on an accelerator opening corresponding to operation of an accelerator pedal by a vehicle operator, and a vehicle speed. A relationship between the accelerator opening and a demanded acceleration is changed based on the minimum generating acceleration which can be generated by the acceleration generator, while maintaining the characteristic of the exponential function of the Weber-Fechner law.
In recent years, vehicles with a by-wire system are known, provided with an operating mechanism which is operated by a vehicle operator, a reaction-force generating mechanism which gives a reaction force of the operation to the operating mechanism, and a driving mechanism which drives the vehicle so that the vehicle is operated by a given response amount according to the operating amount to the operating mechanism. In the vehicles which adopt such a by-wire system, the mechanical coupling mechanism of the operating mechanism and the driving mechanism is replaced with an electrical-signal coupling, and thus, the operating mechanism and the driving mechanism are configured to be independent elements so that the actual operating amount of the operating mechanism by the operator, the reaction force amount to the operator, and the response amount of the vehicle are mechanically separated.
Generally, during operation of a vehicle, the operating states, such as an environmental recognition by the operator, a circumstance judgment by the operator, a device operation by the operator, and a response operation by the vehicle, change in this order. Here, the recognition, the judgment, and the operation are elements which are mainly judged in the operator's sensory area, and the response amount accompanying the behavior of the vehicle is an element which is mainly judged in a physical area. For this reason, a deviation arises between the perceived intensity which the operator senses through vision or somatic sensation and the physical response amount by which the vehicle is actually operated, and a deviation also arises between the perceived intensity which the operator senses through somatic sensation and the physical operating amount by which the operator actually operates the operating mechanism (or the reaction force amount accompanying the operation). That is, in the situation where the operator is operating the operating mechanism of the vehicle, it is necessary to suitably give the perceived intensity in consideration of the operator's sensory characteristic to the operator, with the perception characteristics of the human limbs in mind.
Like the vehicle control device disclosed in JP2011-143915A, when the human perception characteristics are taken into consideration, the linearity of the operator's perceived reaction force and the vehicle behavior can be secured, and a suitable operating feel can be expected by setting a braking characteristic in which the reaction force of the brake pedal and the deceleration of the vehicle have a logarithmic relationship. However, even if such a braking characteristic is set so that the reaction force of the brake pedal and the deceleration of the vehicle have the logarithmic relationship, there is still a possibility that the operator's intention does not match with the vehicle behavior.
During normal travel, since the operator can continuously predict the vehicle behavior through the perceived reaction force when the operator's perceived reaction force and the vehicle behavior are set to have the linear relationship, high operability can be secured. On the other hand, when emergency braking is caused, for example, by a sudden appearance of an obstacle, since the operator's intention is independent of their consciousness before this moment and a higher braking characteristic is demanded, the previous braking characteristic may not meet the response currently demanded by the operator. That is, it is not easy to achieve both the operability by the operator and the response of the vehicle at any operating state.